The smallness of this cross-section is demonstrated by the fact that
if a beam of \(10^{10}\)  neutrinos with \(E\sim 1\)  was aimed at
Earth, only one would be deflected by the Earth's matter. It may seem
then that for neutrinos matter is irrelevant. However, one must take
into account that inccs does not contain the contribution
from forward elastic coherent interactions. In coherent interactions,
the medium remains unchanged and it is possible to have interference
of scattered and unscattered neutrino waves which enhances the
effect. Coherence further allows one to decouple the evolution
equation of neutrinos from the equations of the medium. In this
approximation, the effect of the medium is described by an effective
potential which depends on the density and composition of the matter
[1]}.
